Which party should you vote for to make you happiest?

Each party justifies its policies by appealing to principles like fairness, equality or security. These are hard to object to and harder to choose between. What if, instead, I just wanted to know which party would make me, as the average Briton, happier? Which policies will make people experience more pleasurable, fulfilling, satisfising lives?

In principle, this is a question there could be an objective, factual answer to. Social scientists have been collecting data for 60 years on what makes people happy. Simply, people are asked how they think and feel about their lives. While people do differ in what makes us happy, we differ less than we’d think. Just as no one wants to be in pain, nearly everyone enjoy spending time with their friends and doing fulfilling work. Using the data on happiness, can we establish which polices should make people happier on average. In theory, we could audit the manifestos’ impact on happiness just like the Office of Budget Responsibility does their spending promises.

In practice, it’s not so simple. Doing a precise calculation is immensely complicated. What we can do, and I’ve done here, is a quick and dirty analysis. On the basis of the happiness evidence, we can divide policies into three groups.

The first is those policies that don’t clearly matter to happiness. The top examples are policies to bring economic growth and anything to do with the deficit. Perhaps the most famous result in the happiness data – known as the Easterlin Paradox, named after the economist who noticed it – is that people in developed countries have been getting wealthier, but not any more satisfied with their lives, since World War Two.

While this may seem mysterious, it’s got a fairly obvious explanation. Our happiness is determined by how we feel about what we pay attention to. We adapt to unchanging circumstances and stop paying attention to them. On a daily basis, ordinary people might worry about their work, their family, their health and their commute. What they don’t do is wake up every day a feel grateful they aren’t in a North Korean labour camp. In the same way, rich people don’t focus on how rich they are. That’s why increasing average wealth won’t make the country happier. We can’t neglect economics altogether (as the Greeks or the Zimbabweans could tell us) but wealth doesn’t matter nearly as much we think it does.

Also in this category are foreign affairs, immigration and education. Today, how long did you think about Isis or foreign immigrants for? Was it longer or shorter than you spent thinking about what you should have for lunch? Exactly. Equally, while different education policies may make people smarter, it’s less clear how they’ll increase national happiness. The rule of thumb is that if a policy wouldn’t change something that you’ve done or thought about today, it doesn’t matter.

The second group is policies that do affect happiness, but spending money on them won’t increase it overall because that means you’re taking money from something else. Examples of this include things like spending more on physical health, transport or law and order. If the Tories create 5,000 more doctors, but won’t spend any more overall, and that money comes out the police force or rail infrastructure, the changes cancel each other out.

The third are policies that are really important happiness because they change how people experience their lives. Policies that increase support for mental health and social care, reduce unemployment and lift people out of poverty are those that matter most. To realise why, think of it this way: while breaking a leg might be painful initially, in the modern day it’s really just an inconvenience. However, being depressed, being unemployed or being in poverty are not things you adapt to and stop thinking about.

So, who should you vote for? It depends on your economic views. If you think money grows on trees, vote Green: their support for a guaranteed income, amongst other things, will increase happiness in the short term. If you don’t think money does, vote Lib Dem: their £3.5bn commitment to mental health is the policy with the biggest positive happiness impact. Just behind them are Labour, with the Tories and Ukip’s more right-wing welfare policies putting them in fourth and fifth.

David had taken the same tablets for years. Why the sudden side effects?

David had been getting bouts of faintness and dizziness for the past week. He said it was exactly like the turns he used to get before he’d had his pacemaker inserted. A malfunctioning pacemaker didn’t sound too good, so I told him I’d pop in at lunchtime.

Everything was in good order. He was recovering from a nasty cough, though, so I wondered aloud if, at the age of 82, he might just be feeling weak from having fought that off. I suggested he let me know if things didn’t settle.

I imagined he would give it a week or two, but the following day there was another visit request. Apparently he’d had a further turn that morning. The carer hadn’t liked the look of him so she’d rung the surgery.

Once again, he was back to normal by the time I got there. I quizzed him further. The symptoms came on when he got up from the sofa, or if bending down for something, suggesting his blood pressure might be falling with the change in posture. I checked the medication listed in his notes: eight different drugs, at least two of which could cause that problem. But David had been taking the same tablets for years; why would he suddenly develop side effects now?

I thought I’d better establish if his blood pressure was dropping. I got him to stand, and measured it repeatedly over a period of several minutes. Not a hint of a fall. And nor did he now feel in the slightest bit unwell. I was stumped. David’s wife had been watching proceedings from her armchair. “Mind you,” she said, “it only happens mid-morning.”

The specific timing made me pause. I asked to see his tablets. David passed me a carrier bag of boxes. I went through them methodically, cross-referencing each one to his notes.

“Well, there’s your trouble,” I said, holding out a couple of the packets. One was emblazoned with the name “Diffundox”, the other “Prosurin”. “They’re actually the same thing.”

Every medication has two names, a brand name and a generic one – both Diffundox and Prosurin are brand names of a medication known generically as tamsulosin, which improves weak urinary flow in men with enlarged prostates. Doctors are encouraged to prescribe generically in almost all circumstances – if I put “tamsulosin” on a prescription, the pharmacist can supply the best value generic available at that time, but if I specify a brand name they’re obliged to dispense that particular one irrespective of cost.

Generic prescribing is good for the NHS drug budget, but it can be horribly confusing for patients. Long-term medication keeps changing its appearance – round white tablets one month, red ovals the next, with different packaging to boot. And while the box always has the generic name on it somewhere, it’s much less prominent than the brand name. With so many patients on multiple medications, all of which are subject to chopping and changing between generics, it’s no wonder mix-ups occur. Couple that with doctors forever stopping and starting drugs and adjusting doses, and you start to get some inkling of quite how much potential there is for error.

I said to David that, at some point the previous week, two different brands of tamsulosin must have found their way into his bag. They looked for all the world like different medications to him, with the result that he was inadvertently taking a double dose every morning. The postural drops in his blood pressure were making him distinctly unwell, but were wearing off after a few hours.

Even though I tried to explain things clearly, David looked baffled that I, an apparently sane and rational being, seemed to be suggesting that two self-evidently different tablets were somehow the same. The arcane world of drug pricing and generic substitution was clearly not something he had much interest in exploring. So, I pocketed one of the aberrant packets of pills, returned the rest, and told him he would feel much better the next day. I’m glad to say he did.